Flat composite body, especially a motor vehicle body element

ABSTRACT

A flat composite body with an asymmetric laminar structure generally consisting of a first layer of material, a foam core intermediate layer and a decorative second layer of non-metallic material, wherein a fleece with an epoxy binder is placed between the first and intermediate layers and a fiber matting with an epoxy binder is placed between the intermediate layer and the second layer.

The invention relates to a flat composite body as a vehicle body elementwith an asymmetric laminar structure consisting of a first outer layerof an aluminum material, a steel sheet, or a sintered metal sheet, alsoconsisting of an intermediate layer, in particular a foam core, and asecond inner layer of a non-metallic material.

The invention also relates to a process for manufacture of such a flatcomposite body.

A generic composite body and accordingly a process for manufacture ofsuch composite body is known from the essay “Considerations relating tolarge-series use of sandwich components, their design and configuration,based on the example of the AUDI research vehicle hood” in the series ofstatus BMFT [German Federal Ministry of Research and Technology] statusreports ‘Development trends for motor vehicles and fuels,’ ResearchSurvey 1982, pages 167-177, published by TÜV Rheinland. The essayconcerns itself with light-weight construction in a sandwich design,using a motor vehicle hood as an example. Design, configuration, andmanufacturing considerations indicate the possibilities and limits ofthis light-weight construction principle. Various exemplary embodimentsare shown on pages 171 and 172 in connection with the laminar design. Inone of the embodiment examples the cover layers consist of aluminum orlaminated sheet metal and plastic. This results in an asymmetricallaminar design. The core consists preferably of Structhan(thermoreactive, foamed, fiberglass-reinforced plastic of variablespecific gravity). Structhan assumes the function of stress equalization(prevention of warping).

DE 39 534 C2 describes a process and a support mould for manufacture ofplates and platelike articles such as doors, in particular refrigeratordoors. An asymmetric laminar design is created in this instance as well,with a sheet metal covering layer on one side and a sheet plasticcovering layer on the other and a hard cellular material expanded insitu from a liquid reaction mixture between these two layers. An effortis made to counter the danger of warping due to different thermalexpansion coefficients by subjecting the sheet metal cover layer and/orthe sheet plastic cover layer before expansion to one of the preshapingprocesses which offsets and counteracts the warping which occurs duringcooling. The warping that occurs is not subject to calculation and mustbe determined empirically.

For the sake of clarity, reference is made to WO 83/00840 whichdescribes a composite body, in particular a composite plate for theconstruction of ship walls, container walls or the like with adouble-sided rigid outer layer, a one-part or multi-part foam-core andfiber-reinforced intermediate layers made of fiberglass or the likebetween each outer layer and core as well as hardened plastic forconnecting the entire arrangement. Thereby a symmetrical design isachieved in which each outer layer consists of a material with acompressive strength of approximately at least that of high-gradealuminum.

On this basis the object of the invention is to prepare a flat compositebody as a vehicle body element with an asymmetrical laminar structure oflow weight accompanied by high dimensional stability and high rigidity,along with good paintability.

The solution claimed for the invention lies in a flat composite materialasymmetric in structure having the characteristics specified in claim 1.Claim 7 specifies a process especially well suited for manufacture ofsuch a material. Advantageous configurations and developments of theinvention are specified in the relevant subsidiary claims.

The invention is explained in detail with reference to an embodiment ofsuch a flat composite material, an especially well suited instance ofapplication of which is a self-contained passenger car body part such asa hardtop.

In the drawings

FIG. 1 shows a passenger car without hardtop,

FIG. 2 the same motor vehicle with hardtop installed,

FIG. 3 the hardtop isolated, and

FIG. 4 a sectional diagram of the hardtop along lines IV in FIG. 3.

FIG. 1 presents a sectional view of a passenger car 1 with trunk lid 2,left and right rear fenders 3, 4, left and right vehicle doors 5, 6, andwindshield frame 7. A passenger compartment 8 corresponding to aconvertible is open at the top.

A continuous receiving and fastening mechanism 9 is provided on theedges of the trunk lid 2 and the fenders 3, 4 facing the passengercompartment 8. A corresponding receiving and fastening mechanism 10extends along the upper, horizontally positioned, section of the frame7. Both receiving and fastening mechanisms 9, 10 perform the function ofreceiving a hardtop 12 as shown in FIG. 2, so that the passengercompartment 8 may now be closed at the top. Hence the hardtop 12 may beinstalled or removed as desired, so that the passenger car 1 may bedriven optionally with the corresponding equipment.

For the sake of clarity the hardtop 12 is again shown separately in FIG.3, while the laminar structure of this asymmetric flat composite elementis to be seen in FIG. 4. The outer layer 13 is made of a preformed blankof an aluminum material; in this instance as well use may be made ofsheet steel or a sintered metal, for example. Adjoining this outer layer13 is nonwoven polyester material (fleece) 14 provided with an expandedepoxy resin bonding agent. An inner layer 15 on the passengercompartment side is in the form of decorative material next to which inturn is fiber matting 16 provided with an expanded epoxy resin bondingagent. The cavity is filled with a polyurethane (PU) foam core 17;consideration may also be given to use of an EPS core, other light foammaterials (polypropylene, etc), or a core of blown glass with bondingagent. Inserts 18, for example ones also of a an aluminum material, maybe provided at suitable points inside the cavity and may be connected tothe outer or inner layer 13, 15 by means of a screw connection 19.

The flat composite material, the hardtop 12 shown in the exemplaryembodiment, consists preferably of a metal surface, nonwoven polyestermaterial (fleece) which may be a common commercial product such as isused in kitchen vapor filters, a foam core of average density(approximately 20 kg/m³ to approximately 100 kg/m³), fiber matting(randomly distributed chopped glass fiber matting with a finishpreferably suited for epoxy resins, optionally containing athermoplastic binder for thermal deformation), and a decorativemultilayer foil, preferably with a PUR barrier layer. Suitable asdecorative foil materials in particular are thermoplastic foils with anintegrated barrier layer (intended to prevent foam breakthrough in presscompaction), but also natural products such as leather, for example, ifit withstands a foam pressure of about 1.5 bar without breakthrough.Nonwoven polyester and staple fiber matting are additionally moistenedwith expanding epoxy resin.

The specific laminar structure is presented below:

Sheet aluminum (alkaline cleaned); sheet thickness 1.1 mm

Polyester fleece, 300 g/m²

PU foam core with sg (specific gravity) approximately 54 kg/m³

Chopped glass strand fiber mat: 450 g/m²

Polyurethane decorative fabric: 70 μm foil barrier,

whereby an expanding matrix system acting as binder, with a reactiveresin mass (total amount of resin+hardener+propellant) of 1600 g/m²(outer) and approx. 1300 g/m² (inner) is further specified as follows:

Resin: Araldit®LY 5054 (made by Ciba Spezialitätenchemie AG, Basel)+1%propellant

Hardener: XB 5003-1® (made by Ciba Spezialitäitenchemie AG, Basel)

Propellant: DY 5054® (made by Ciba Spezialitätenchemie AG, Basel)

Mixture ratio: 100:20% by weight components,

whereby it is possible to expand the reactive resin mixture and theresulting foam does not collapse when the separating agent, based onPAT® 921/A, made by the Wüirtz Company, is used.

In theory all liquid epoxy resin systems which can react to ahardener/hardener mixture are suitable as an expanded matrix systemserving as bonding agent. Preference is given for this purpose tobisphenol epoxy resins such as bisphenol-A and bisphenol-A/F epoxidesmodified with stabilizers and thixotropic agents. Also suitable areglycidyl ethers of aliphatic alcohols or polyalkylene glycol, as well assolid epoxy resins which may be processed in the liquid state when mixedwith a liquid epoxy resin; bisphenol-A epoxy resins, for example, may beemployed as solid epoxy resins.

Theoretically all known liquid hardeners may be used as hardeners, forexample, aliphatic, cycloaliphatic amines and their adducts withepoxides, for example, as well as polyamide amines. Other additiveswhich promote hardening, e.g., tertiary amines, may be used in themixtures, depending on the epoxy resin systems.

The fleece to be used in accordance with the invention serves thepurpose of so-called back tension which equalizes stresses resultingfrom asymmetry. Consequently, the fleece must vanish during thehardening process. Examples of fleeces are thermoplastic fleeces, withfleeces made of thermoplastic polyesters being preferred. Theoreticallyall common fibers such as those of glass, carbon, kevlar, and naturalfibers may be used. Glass strand fibers present the advantage that theycan be thoroughly mixed with foam; in theory all fiber glass fabrics andcomplexes may be used.

The following process is carried out in manufacture of the flatcomposite material (hardtop 12) claimed for the invention.

First the outer layer 13, such as an aluminum plate, is worked with asuitable deep-drawing die into the subsequent shape of the hardtop 12and the edge outlines are then cut (by laser cutting, for example). Thesurface of the blank is then subjected to alkaline degreasing to improveadhesion. The alkaline degreasing consists preferably of the stepsrepresented by degreasing, rinsing, caustic passivation, rinsing,drying. The process may be continued with cataphoresis priming,optionally in the dipping process (KTL), in addition to anticorrosivecoating such as zinc phosphating.

The PU foam core 17 provided between the inner and outer layers 13, 15is foamed in a suitable tool before the individual composite layers areassembled and bonded. The foam blank is then wrapped in fiber matting 16and fleece 14 and wetted with expanding epoxy resin.

To bond the individual layers together and accordingly produce thehardtop 12 in a single operation a suitable compression molding die isused to introduce the preformed outer layer 13 into the die matrix, theinner layer 15 (decorative layer) is stretched over the die stamp, andthe foam core 17, positioned opposite the outer layer 13, is alsoinserted into the die matrix. The die mold is then closed by appropriatemovement of the stamp accompanied by pressing of the individual layersand simultaneous hardening.

Since the expansion relationships among the individual layers have beencoordinated with each other, a dimensionally stable composite materialis obtained. Stability of shape is achieved especially when epoxy resinis used in that no contraction occurs in the liquid phase as a result ofexpansion except for the negligible cooling contraction. The volume ofthe foam system must be maintained until jelling takes place.

Experiments have been conducted which show it to be advantageous if thecompressive molding dies are at a temperature of approximately 40 to 50°during pressing of the individual components of the flat compositematerial. Good results have been obtained with a pressing time of around60 minutes. Other temperatures and pressing times are conceivable. Thecompressive molding dies should be suitably adjustable.

The result obtained is a flat composite material possessing theadvantages indicated above, along with good paintability of the metalsurface (outer layer 13).

It is also possible during the manufacturing process to build hollowpipes for later cabling in the cavity later filled with PU foam core.Fastening elements such as bolt-on plates or inserts may also be used.Nor is the invention restricted to the application (hardtop) indicatedin the exemplary embodiment. Application for other vehicle elements,including ones for rail vehicles and for decorative design elements,spherically shaped facade elements, elements for construction of fairsand exhibitions, and the like, is also conceivable.

This process may be used in particular wherever a metal surface isneeded and low component weight is an advantage. Examples are machinebuilding (moving masses), boat building, aircraft, athletic equipment,interior finishing, panels, facades, furniture, etc.

What is claimed is:
 1. A flat composite body with an asymmetric laminarstructure comprising: a first layer of metallic material; a foam coreintermediate layer; and a decorative second layer of non-metallicmaterial; wherein a fleece with an epoxy binder is placed between thefirst and intermediate layer and a fiber matting with an epoxy binder isplaced between the intermediate layer and the second layer.
 2. The flatcomposite body according to claim 1 wherein the first layer is analuminum plate, the fleece is polyester, the foam core intermediatelayer has a medium density of 20 kg/m³ to 100 kg/m³ and the second layerhas a decorative multi-layer foil with a barrier foil.
 3. The flatcomposite body according to claim 1 wherein: the first layer is analuminum plate having a thickness of about 1.1 mm; the fleece is made ofpolyester and has a mass per square meter of 300 g/m²; the intermediatelayer is made of a polyurethane foam core having a specific gravity of54 kg/m³; the fiber matting is chopped glass having a mass per squaremeter of 450 g/m²; and the second layer is a polyurethane decorativefabric having a 70 μm barrier; wherein an expanding matrix system isused as the epoxy binder to bind layers together having a reactive resinmass of 1600 g/m² between the first layer and the polyester fleece and areactive resin mass of 1300 g/m² between the second layer and the fibermatting and the polyurethane foam core does not collapse with the use ofa separating agent.
 4. The flat composite body according to claim 1wherein the intermediate layer is made of a polypropylene or an EPScore.
 5. The flat composite body according to claim 1 wherein theintermediate layer is made of blown glass with a binder.
 6. The flatcomposite body according to claim 1 wherein the first layer is made of asteel plate or sintered metal.
 7. The flat composite body according toclaim 1 wherein inserts are connected one or both of the first andsecond layers and extend into the intermediate layer.
 8. The flatcomposite body according to claim 7 wherein the inserts are made ofempty pipes, rods, or plates.
 9. The flat composite body according toclaim 1 wherein the fleece is a kitchen vapor filter, thermoplasticpolyester, or woven fabric.
 10. The flat composite body according toclaim 9 wherein fibers of the fleece are made of glass, carbon, kevlar,or natural fibers.
 11. The flat composite body according to claim 1wherein the second decorative layer is made of a thermoplastic foil withan integrated barrier foil.
 12. The flat composite body according toclaim 1 wherein the second decorative layer is leather.
 13. The flatcomposite body according to claim 1 wherein the epoxy binder comprises abisphenol epoxy resin with stabilizers and thixotropic agents.
 14. Theflat composite body according to claim 1 wherein the epoxy bindercomprises a glycidyl ether of alophatic alcohols or polyalkylene glycol.